Lead alloy for cable sheathing



United States Patent LEAD ALLGY FDR ABLE SEEATHYNG John F. Ecirel, Scotia, N. Y., assignor to General Eiectric Company, a corporation of New York No Drawing. Application September 9, 1952, Serial No. 308,709

2 Ciaims. (531. 75-466) The present invention relates to a lead base alloy particularly suitable for use as a cable sheath and to cables sheathed with such an alloy.

While one of the original purposes for the lead sheath which is extruded around electric power and communication cables was to provide a durable protection against moisture, the requirements for the lead sheath on presentday cables, particularly the gas-filled and oil-filled cables, are such that moisture resistance is only one of many factors which must be taken into consideration in selecting a suitable lead alloy. In present-day cables, the lead sheath must have good bursting strength in order to resist the pressure which may be built up at certain sections within the cable as, for example, by the concentration of the oil filling at a low point in the cable with resultant development of a high hydrostatic pressure. Another important factor in the selection of a lead sheathing alloy for fluid-filled or other cables is good bending life or bending fatigue strength such that the sheath will be capable of withstanding repeated and substantial bending resulting, for example, from changes in temperature or from vibrations.

The present invention is based on the discovery that an improved cable sheathing possessing good bending life and tensile strength can be obtained by employing a cable sheathing lead base alloy essentially containing small amounts of aluminum and zinc or aluminum, zinc and tellurium. More specifically, it has been found that alloys containing, by weight, from about 0.03 to 0.08% aluminum, from about 0.03 to about 0.15% zinc and from 0 to about 0.1% tellurium, bflance lead, are particularly useful as cable sheathing. The term balance lead is intended to cover lead containing small amounts of impurities such as antimony, copper, bismuth, silver and iron present in commercial leads, the presence of which, in impurity amounts, is not detrimental to the present invention. Preferred alloys are those containing about 0.07% aluminum and about 0.1% zinc. The

cable sheathing alloys of the present invention are hardened lead alloys particularly characterized by good tensile strength and good bending life under higher strain conditions so that cable sheaths of the subject alloys are characterized by improved service life, particularly at the more elevated operating temperatures.

The advantageous properties of the alloys of the present invention are evident from the following test results. Strip samples of an alloy containing 0.07% aluminum and 0.1% zinc, balance lead which had been extruded at about 200 C. and air cooled, possess an average tensile strength of 2400 p. s. i. and an elongation of 50%. Repeated bending tests at F. at approximately 0.5% strain and one cycle per minute on strip samples of this alloy were also carried out. The alloys averaged approximately 22,000 cycles to failure. Similar tests on an alloy composed of .076% aluminum, .09l% zinc, .O73% tellurium, balance lead, gave an average tensile strength of 2450 pounds per square inch and 50% elongation and 22,000 cycles to failure in the bending life tests. As is evident from the tensile strength and elongation values, the alloys possess both a high strength and a high degree ductility not normally obtainable together in a lead base alloy.

From the results of the above tests, it will also be noted that the tellurium addition has a slight effect on the tensile strength or the resultant alloys but has practically no etfect On the bending life of the alloys. it, therefore, constitutes a permissible but not an essential component of the alloy. However, in this connection it is essential that the alloy be free or substantially free from efiective amounts of other alloying ingredients which alone or in combination with the aluminum or zinc may deleteriously aifect the desirable properties of the base alloy.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A lead base alloy consisting of from 0.02 to 0.08% aluminum, 0.03 to 0.15% zinc, balance lead, and small amounts of impurities present in commercial leads.

2. A lead base alloy consisting of from 0.02 to 0.08% aluminum, 0.03 to 0.1% zinc, up to 0.1% tellurium, balance lead, and a small amount of impurities present in commercial leads.

References Cited in the tile of this patent UNITED STATES PATENTS 1,892,273 Hawkins Dec. 27, 1932 2,525,603 Jenks et al. Oct. 10, 1950 FOREIGN PATENTS 449,372 Great Britain June 25, 1936 570,041 Great Britain June 20, 1945 

1. A LEAD BASE ALLOY CONSISTING OF FROM 0.02 TO 0.08% ALUMINUM, 0.03 TO 0.15% ZINC, BALANCE LEAD, AND SMALL AMOUNTS OF IMPURITIES PRESENT IN COMMERCIAL LEADS. 